In yet another sign of trouble for Air America Radio, the liberal talk network's co-founder and chairman, Evan Cohen, resigned Thursday along with his investment partner and vice chairman, Rex Sorensen.

The company also failed to make its scheduled payroll Wednesday, leaving its staff of roughly 100 writers and producers unpaid until Thursday.

The radio network has been on the air for only five weeks. On April 30, it was pulled off Chicago's airwaves because of a payment dispute.

"We're on a wild ride," said Jon Sinton, the network's president, acknowledging that Air America has suffered "the typical bumps and bruises faced by any start-up."

"But the bottom line," he said, "is that we are on the air to stay."

The departures of Cohen, a former Republican political operative from Guam who was among the network's initial investors, and Sorensen, an investor, mark the second executive shake-up at the fledgling network in as many weeks.

Replacements for Walsh and Cohen have yet to be named. Asked when those positions would be filled, Sinton replied: "I wouldn't hold my breath."

Sinton said Cohen was forced to resign by investors unhappy with the way he handled a clash with Multicultural Radio Broadcasting Inc., owner of Air America's Chicago and Los Angeles stations.

After an acrimonious and public dispute, the two companies severed their relationship, leaving the network off the air in two of the nation's top three markets. (Air America remains on the air in 16 markets, including New York City.)

"I think that other shareholders were upset with the way that escalated so quickly," Sinton said. "I don't think that needed to be handled in such an argumentative fashion."

Cohen has previously said that Air America's investors include former broadcasters Thomas Embrescia and Norman Wain, TV pioneer Norman Lear, and Sheldon Drobny, the Highland Park entrepreneur who originally founded the company before selling most of it to Walsh and Cohen in November.

Sinton said he was unaware whether Cohen and Sorensen will retain their ownership stakes in the company. Cohen did not return phone calls.

Last week, according to two sources familiar with the matter, paychecks to some of the network's talent--a group that includes Al Franken, Janeane Garofalo, and Randi Rhodes--bounced, and Rhodes joked on the air about not being paid.

A scheduled payday for the staff on Wednesday came and went without checks, though the staff was paid on Thursday. Sinton chalked up both cases to "technical issues."